This invention relates to a color copier operable both in monochromatic and full-color copying modes and, more particularly, to such a color copier which allows the quality of its copy image to be quickly and easily adjusted both in the monochromatic and full-color copying modes of operation.
With the recent progress in the technologies related to electrophotographic copiers, there are now being developed color copiers capable of forming full-color pictorial images. Such a color copier is provided, for example, with color filters for separating reflected light from an original document to be copied into light beams of three primary colors (blue, green and red) and three developing devices using toners of their complementary colors (yellow, magenta and cyanic) and forms a full-color image by repeating the process of forming a toner image three times. To explain this process more in detail, blue light is used to form a yellow toner image, green light is used to form a magenta toner image, red light is used to form a cyanic toner image, and these three toner images are superposingly transferred onto a single sheet of paper to form a full-color copy image.
Most full-color copiers of this type can be operated also in a monochromatic copying mode wherein a copy image is formed either in black or in one of the aforementioned three primary colors. When such a copier is operated in a monochromatic copying mode, the image quality is usually controlled on a real-time basis, as done by prior art black-and-white copiers, by detecting the condition of the original during the copying process and setting the conditions of copying such as exposure on the basis of the detected data. When this copier is operated in a full-color copying mode to superpose a plurality of toner images, however, adjustments of image quality are complicated, including color corrections according, for example, to the particular color characteristics of the original. In other words, image quality cannot be adjusted by a real-time control and exposure, photoreceptor surface voltage and bias voltage of the developing device are manually set. Typically, the operator conducts a series of tests by varying the photoreceptor surface voltage, etc. and manually sets the exposure, the photoreceptor surface voltage, etc. to appropriate values.
In summary, when a full-color copier is operated in a full-color copying mode, real-time control of the type used in the monochromatic copying mode of operation cannot adjust the image quality adequately. On the other hand, manual adjustments are time-consuming and economically disadvantageous because many copying operations must be repeated. Moreover, manual adjustments require a skilled operator and less experienced persons cannot be expected to perform them adequately. A full-color copier may be provided only with a means for automatically adjusting the image quality when it is operated in a full-color copying mode, such a copier is inefficient, requiring an unreasonably long time for the adjustment of image quality when operated in a monochromatic copying mode.